chan_agent: Fix wrapup time wait response.

* Made agent_cont_sleep() and agent_ack_sleep() stop waiting if the wrapup 
time expires.  agent_cont_sleep() had tried but returned the wrong value 
to stop waiting.  

* Made agent_ack_sleep() take a struct agent_pvt pointer instead of a void
pointer for better type safety.
........

Merged revisions 378486 from http://svn.asterisk.org/svn/asterisk/branches/1.8


git-svn-id: http://svn.asterisk.org/svn/asterisk/branches/11@378487 f38db490-d61c-443f-a65b-d21fe96a405b